In our application for U.S. patent Ser. No. 12/692,688, “Optical Device Using Diffraction Gratings”, filed Jan. 25, 2010, we show how a single-groove diffraction grating with periodic elements of uniform width can be used to couple first order diffraction components of normal s-polarized incident light into a substrate at angles greater than the critical angle of the substrate boundary thereby to cause the refracted light to propagate through the substrate.